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Bird legs as key to evolutionary success
From: Ben Creisler
A new paper that may be of interest:
Anick Abourachid and Elizabeth Höfling (2012)
The legs: a key to bird evolutionary success.
Journal of Ornithology (advance online publication)
2012, DOI: 10.1007/s10336-012-0856-9
Birds are the most diverse and largest group of extant tetrapods. They
show marked variability, yet much of this variation is superficial and
due to feather and bill color and shape. Under the feathers, the
skeleto-muscular system is rather constant throughout the bird group.
The adaptation to flight is the explanation for this uniformity. The
more obvious morphological adaptations for flight are the wings, but
the trunk is always rigid, the tail is short and the neck is flexible,
since all these features are correlated with flying behaviour.
Unrelated to the exigencies of flight, the legs always have three long
bones, and all the birds walk on their toes. This leg structure is a
striking plesiomorphic feature that was already present in related
dinosaurs. The multi-purpose potential of the legs is the result of
the skeletal architecture of a body with three segmented flexed legs.
This configuration provides mechanical properties that allow the use
of the legs as propulsive, paddling, foraging or grooming tools. It is
the association of diverse modes of locomotion—walking, running,
hopping, flying and swimming—that have enabled the birds to colonize
almost all the environments on Earth.